The antithrombotic action of the acetylsalicylic acid is known (Med. Klin., 76, 692/1981) but the optimum dosage is still open to debate. Recommendations vary between 300 mg/day and 3.times.500 mg/day or 4.times.325 mg/day. Acetylsalicylic acid brings about an irreversible inhibition of cyclooxygenase, an enzyme which produces thromboxane A.sub.2 (TXA.sub.2) in the thrombocytes. Without TXA.sub.2, no arrest of hemorrhage, as desired effect, takes place and no aggregation of the blood platelets which is necessary for thrombogenesis. At the same time, however, acetylsalicylic acid also inhibits the cyclooxygenase of the intima of the blood vessels so that the endogenic aggregation inhibitor epoprostenol, PGI.sub.2, cannot be formed. In this way, acetylsalicylic acid obtains a thrombogenic potency. Since the cyclooxygenase of the thrombocytes is more sensitive towards acetylsalicylic acid and is more slowly regenerated as that of the inner blood vessel walls, it is assumed that a certain differentiation of the acetylsalicylic acid effect can be achieved via the dosage.
On the one hand, because of the reduction of the acetylsalicylic acid side effects, which can be considerable and manifest themselves, especially in the gastrointestinal tract and in the kidneys, and, on the other hand, for the above-mentioned reasons, it is of decisive therapeutic importance to keep the dosage of the acetylsalicyclic acid as low as possible. For the purposes of the present invention, this is achieved by a combination of acetylsalicylic acid with diltiazem.